First it has to draw the image. Then it has to turn itself upside down and shake itself like crazy to clear the image. Then it has to draw the new image.

It goes like this:

-All white
-Draw the page
<wait until it's time to go to the next page>
-Invert image
-All black
-All white
-Draw the page

This makes it look like it's flashing. I suppose that if any errors are encountered in the process then it redraws the same page a second time to make sure. I can see how this could be considered abnormal or unusual but really it's normal.